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X Chromasome on Family Finder

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  • X Chromasome on Family Finder

    Hi, can someone guide me please on the chromasome matches on Family Finder and the X chromasome at the bottom of the list. Am I understanding this right, that this is not the female X-chromasome. I have some matches on the autosomal test I uploaded from Ancestry which show as an 'X' match, can I assume that these matches are on my maternal side, or is this something else. I understand about X and Y chromasomes being female and male respectively, but I'm confused about this.

  • #2
    Way back in 2013, I posted some links about the X chromosome, in the then-new FTDNA subforum for it. See "Resources about the X-Chromosome." I suggest you look at the links in the "Charts" section of that post. ISOGG has a page on X chromosome testing with many links. Your matches on the X may be male or female. A good page to start with is "X DNA's Helpful Inheritance Patterns." Check out the charts on that page illustrating the different X inheritance patterns for males and females.

    The X chromosome has a unique inheritance pattern, and there are more ancestors for females who are in that pattern than there are for males, because females have two X chromosomes. To determine which of your ancestors could possibly have passed on an X chromosome to you, use some of the blank charts (links for those in the first link above) and enter your own appropriate ancestors. A video on YouTube may help: "Is X-DNA helpful in genetic genealogy? - A Segment of DNA," but it would be best to review the charts and pages on the pages linked above before viewing it, so as not to get confused.

    Keep in mind that FTDNA will show a match as an X match, even if the segment total is very small. One point to keep in mind about matching X segments is that they need to be larger than matching segments on other chromosomes, twice as large actually, to be considered useful for genealogy. Therefore, if you normally use 7-10 cMs as the minimum for matches on chromosomes 1-22, you should use 15-20 cMs as a MINIMUM for an X-match. Most of the X-matches in your Family Finder Matches list will not be above 15 cMs, so use caution in your assumptions.

    When you select a match shown as an X-match from your Family Finder list to compare in the Chromosome Browser, you can check the size of the X chromosome matching segment(s) by clicking on "Detailed Segment Data," and checking the amount of each X segment (if more than one).


    • #3
      Thank you for your help on this, I have printed out the charts so hopefully I will be able to make some sense of it all.


      • #4
        All sites handle X differently
        • FTDNA shows an X match ONLY if there is also an autosomal match. As mentioned by KATM, most FTDNA X matches are too small to be significant.
        • 23andMe shows all X matches and totally integrates them with the automosal, which is actually a bad idea. But you will see X-only matches that FTDNA skips
        • GEDMatch shows all X matches but keeps them in separate columns and categories, away from the autosomal.
        • My Heritage and AncestryDNA ignore XDNA completely, although it is in their Raw Data. Ironically, AncestryDNA tests the most X SNPs by a pretty fair margin

        Females get lots more X matches than males, although most are gibberish.

        XDNA has nothing to do with mtDNA. Although the mtDNA pathway is one of the many X pathways. Actually the mtDNA pathway is the weakest X pathway.

        Personally I prefer the X fan charts. And probably the ones with percents, although XDNA is semi-random enough to make the percents only a very general guide. Google "XDNA fan chart"


        • #5
          My advice is to not try and figure out something more than a couple of generations back with analyzing the X. There is a lot about the X that even the experts don't understand.


          • #6
            There is a lot I don't understand as I haven't done this before, and a lot I'm learning at the same time. Hopefully, when my Y111 finishes analysing thing may be a little clearer.